Being the keeper of the ancient commentaries I decided to look at what some of
the old boys had to say about this. Henry Alford agrees with you as does H. A.
W. Meyer. A. Plummer waffles a little but he is leaning toward your reading.
A.B. Bruce prefaces his remarks by saying that seeing MEIZON as a reference
to Christ is the "almost unanimous opinion of interpreters ancient and
modern." Having said this A.B. Bruce then suggests that Jesus might be
thinking of the Kingdom here rather than the King.

My personal opinion is without much weight, but I think that A.B. Bruce has a
good point. I think that the viable alternatives are two, MEIZON refers either
to the Kingdom or to the King. From my study of Matthew I would conclude that
the theme of the book is the Coming of the Kingdom of God.

As for the neuter being used, this presents no real problem. The neuter
adjective when it stands for an absolutized abstract quality (a what?) does
not need to agree in gender with it's ultimate referent. This is a little
grammar on the fly which will probably result in shrieks of outrage from the
serious grammarians on the list. Also, Jesus was in the habit of using
somewhat opaque indirect references to his role as the Messiah, and this would
fit well into that pattern.